This invention relates generally to semiconductor processing methods and apparatus and, more particularly, to a method and apparatus for handling of semiconductor wafers during processing.
One of the primary concerns in the manufacture of semiconductor devices, such as integrated circuit chips, is avoiding contamination from particulate matter which may fall onto or otherwise be deposited on a top surface or face of a semiconductor device. The manufacture of semiconductor devices includes multiple fabrication steps such as masking, etching, electroplating, chemical mechanical planarization and polishing, oxidation and dielectric layer deposition on a semiconductor wafer. Between these various process steps, the wafer may be picked up by a mechanical handling apparatus and moved to temporary storage. In some applications, a plurality of wafers may be collected and stored in a storage cassette between processing steps.
As shown in FIG. 1, a semiconductor wafer storage cassette includes a plurality of wafer support elements arranged to receive and support a plurality of stacked wafers. In one form, support elements engage wafers at their outer edges and support the wafers in horizontal, spaced planes. A robotic wand may be used to insert the wafers into and remove the wafers from the cassettes. To remove a wafer from a processing station, the wand engages the wafer using vacuum or other known means, then lifts and moves the wafer to the cassette where the wafer is stored until it is needed for a next processing step.
It is known that semiconductor-manufacturing areas must be maintained in an extremely clean condition in order to minimize the contamination of the wafers being processed. In spite of such efforts, particulate debris cannot be completely eliminated, and some semiconductor devices on some wafers must be scrapped as a result of particulate contamination. Accordingly, it is advantageous to provide apparatus and/or methods for reducing opportunities for contamination of semiconductor wafers during the manufacturing process.
Applicants have discovered that a possible source of contamination is debris that may accumulate on a backside of a semiconductor wafer during processing and which can then fall onto a face of another wafer when the wafers are stored in a stacked position between processing steps. The present invention addresses this potential source of contamination by changing how such semiconductor wafers are stored within storage cassettes between processing steps. In one form of the invention, wafers are stored in conventional cassettes but in an inverted position so that the wafer face is oriented downward. Accordingly, any debris falling under the force of gravity will land on a backside of the wafer where such debris will not affect the circuit formed on the face of the wafer. The invention further includes adapting the wafer handling apparatus, such as a vacuum wand, with a rotatable section to enable inversion of the wafer between processing equipment and storage. More particularly, the wand is adapted to rotate the wafer through 180 degrees in order to position the wafer in an upside down orientation in the storage cassette whereby, if contaminants do drop from a wafer in a cassette, the particles will fall on the backside of a lower stacked wafer. In one form, a rotary coupling enables the wand head of the handling device to rotate through 180 degrees, and/or rotate to a plurality of positions between a position of the wafer facing upward and upside down.
It is also contemplated that the wafers could be on one edge in a different form of cassette such that the wafers would only be rotated 90 degrees.